Systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) are rheumatic diseases characterized by hypergammaglobulinemia and the production of auto-reactive antibodies. We propose to quantitate in vitro immunoglobulin synthesis by lymphocytes from patients with these diseases and determine the fraction of immunoglobulin synthesis involved in autoantibody production. The in vitro synthesis of immunoglobulin and autoantibody by lymphocyte populations enriched or depleted of specific cells reactive with "autoantigen" by affinity chromatography will be examined. Autoantibody producing lymphocytes will be enumerated by plaque forming cell (PFC) and rosette forming cell (RFC) techniques. Bone marrow derived lymphocytes (B lymphocytes) will be identified by immunofluorescence with anti-immunoglobulin antisera and thymic derived lymphocytes (T lymphocytes) by enumeration of "E" rosettes and immunofluorescence with heterologous anti-human brain antisera. T cell function will be evaluated by macrophage migration factor (MIF) assay, mixed lymphocyte culture (MLC) and lymphoblast transformation induced by non-specific mitogens and specific antigens. These studies will be performed serially in patients with SLE and RA and correlated with the clinical assessment of the disease course and response to therapy.